Seat belt retractors with electromotive drives are known in particular as reversible seat belt tensioners which upon activation in a pre-accident phase, pull out any slack present in a safety belt of a seat belt device.
Furthermore, it is also known from DE 43 32 205 C2 how to use the electromotive drive (electric motor) to retract the seat belt in the park position. The electromotive drive is thereby controlled as a function of the insertion state of the belt tongue.
Also provided in the seat belt retractor is a retraction spring which exerts a return force on the seat belt independently of the action of the electromotive winding aid. This return force should for reasons of comfort be as light as possible in the emplaced condition of the seat belt, wherein it must nonetheless be ensured that the seat belt upon removal is reliably wound up in the park position.
Furthermore the retraction springs are subject to basic aging processes, so that the return force of the retraction springs decreases with increasing operating life and the associated high number of use cycles.
The object of the invention is to create a seat belt retractor with an electromotive winding aid which features increased user comfort and enables winding of the safety belt in the park position independently of the return force of the retractor spring, even after a high number of use cycles. In addition, the object of the invention is to create a procedure to control an electromotive winding aid of a seat belt retractor which facilitates improved winding of the seat belt in the park position.
To attain the object, the invention proposes a seat belt retractor and a procedure described herein.
In keeping with the basic idea of the invention it is proposed that the electromotive winding aid can be controlled as a function of the seat belt feed rate. The seat belt feed rate is the parameter that directly characterizes the retraction movement and results from the return force of the retractor spring. In the case where the retractor spring cannot exert the required return force and the seat belt feed rate does not as a result exceed a predetermined boundary value, the electromotive winding aid is activated to support the winding movement of the seat belt so that in this case, too, the seat belt is wound securely.
It is further proposed that the electromotive winding aid is controllable as a function of the current consumption of the winding aid. For the case that the occupant, for example, holds on to the seat belt and thereby impedes the winding movement, the current consumption of the winding aid increases above a predetermined limiting value. In this case the winding aid is deactivated for its own protection.
It is proposed according to one other preferred embodiment of the invention that a memory unit is provided in which various control profiles are stored and the electromotive winding aid is controllable depending on whether the predetermined use cycles of the seat belt controller are exceeded and/or as a function of the sensed ambient temperature according to various control profiles. It has been shown that the return force of the retractor spring decreases with an increasing number of use cycles because of aging and, in addition, is dependent on the ambient temperature. To compensate for these changes of the return force, various control profiles are stored in the memory unit and then serve to control the winding aid when the corresponding parameters are sensed. These control profiles can include various return forces or also return force curves, so that the total return force from the return force of the retractor spring and the winding aid is then constant independently of the aging of the retractor spring and the ambient temperature or corresponds to a predetermined curve.
According to another preferred embodiment of the invention it is proposed that the electromotive winding aid is additionally controllable as a function of the insertion state of a belt tongue lockable in the seat belt lock. By means of the insertion condition of the belt tongue, the buckling or removal of the seat belt can be recognized with certainty. Furthermore, by means of a changing insertion condition of the belt tongue, a conclusion can be drawn about a use cycle, the sum of which allows an indirect conclusion about the aging status of the retractor spring.
It is further proposed that the seat belt retractor have a retractor spring pretensioning the belt shaft in the winding direction, which has a return force of less than 1 N. The proposed small return force facilitates very pleasant wearing comfort of the seat belt for the occupants, wherein the small return force is then increased by means of support from the winding aid to a higher return force to retract the seat belt, and the seat belt is securely wound in the park position.
Furthermore, to achieve the object, a procedure to control an electromotive winding aid of a seat belt retractor is proposed in which the electromotive winding aid is activated when a belt lock sensor senses that the belt tongue is not locked, and a sensor device for sensing the seat belt feed rate senses a seat belt feed rate that is below a predetermined boundary value.
A removed seat belt can be recognized in a first step from a non-locked seat belt tongue. If the seat belt feed rate then does not exceed the predetermined limiting value, it can be concluded that the return force of the retractor spring is not sufficient to wind the seat belt into the park position. In this case the winding aid is then activated and the seat belt is wound with certainty with the support of the winding aid.
It is further proposed that the electromotive winding aid is deactivated if the sensor device to sense the seat belt feed rate senses a seat belt feed rate below a predetermined boundary value and/or the current consumption of the electromotive winding aid exceeds a predetermined boundary value. From the undershooting of a predetermined boundary value of the seat belt feed rate, attainment of the park position, for example, can be sensed, since the seat belt feed rate is equal to zero in the park position and reduced very drastically shortly before reaching the park position and thereby undershoots the predetermined boundary value. Alternatively the winding aid is also then deactivated, if the occupant, for example, holds the seat belt and the current consumption of the winding aid as a result exceeds a predetermined value.
In keeping with another preferred embodiment of the invention it is proposed that a sensor device to sense parameters which characterize the aging condition of a retractor spring pretensioning a belt shaft of a seat belt retractor in the winding direction is provided and the electromotive winding aid is controlled as a function of the aging condition of the retractor spring according to various control profiles. For example, the sensing device can be a belt lock sensor whose insertion procedures are selected in an evaluation unit. In addition, the sensor device can be a position sensor directed at the retractor spring itself. which senses the position of the retractor spring. For the case where a conclusion can be made directly or indirectly about the aging of the retractor spring because of the sensed parameters or the use cycles and a diminishing return force, this diminishing return force is compensated for by control of the winding aid on the basis of an individual control profile provided for this case. This control profile can be formed by a return force of the winding aid increased by a constant factor or by a changed parameter with an individually adapted curve of the return force exerted by the winding aid.
It is further recommended that a sensor device to sense the ambient temperature is provided and the electromotive winding aid is controlled as a function of the ambient temperature according to various control profiles. The return force of the retraction spring can vary independently of its aging status because of the ambient temperature. This change of the return force can then be compensated by the corresponding support of the retraction movement by the winding aid such that the seat belt can again be wound with certainty using a predetermined minimum return force.